1. Field of the Invention
The present invention relates to a developing device and an image forming apparatus.
2. Description of the Related Art
Conventionally, copying machines, printers, facsimiles, or the like are known as an electrophotographic image forming apparatus. These image forming apparatuses form an electrostatic latent image on the surface of a photoreceptor drum (toner image bearing member), supply a toner to the photoreceptor drum using a developing device to develop this electrostatic latent image, transfer a toner image on the photoreceptor drum to a recording medium such as a recording paper, using a transfer part, and fix the toner image onto the recording paper using a fixing device, thereby forming an image.
As a conventional developing device, there is a circulation-type developing device like a developing device disclosed in Japanese Unexamined Patent Publication JP-A 2005-24592, including two developer conveying passages through which a toner is circulated and conveyed, and two conveying members which convey the toner in the developer conveying passages. In such a conventional developing device, the toner is charged by the conveying members, the charged toner is borne on the surface of a developing roller provided in the developing device, and the toner is supplied to an electrostatic latent image from the developing roller by an electrostatic attraction force. The conventional developing device'forms the toner image on the photoreceptor drum in this way.
However, in the above developing device, the conveying member is constituted by a rotating shaft, and a spiral blade which is a stretch of conveying blade. Thus, the toner is blocked by the spiral blade and is not easily diffused in an axial direction of the rotating shaft. Therefore, when a toner is consumed locally or a new toner is supplied, there is a problem in that unevenness occurs in the concentration of the toner in the developer conveying passages. As a result, there is a problem in that unevenness of image density occurs in a formed image.